Container cranes are used to handle freight containers and especially to transfer containers between transport modes at container terminals, freight harbours and the like. Standard shipping containers are used to transport a great and growing volume of freight around the world. Transshipment is a critical function in freight handling. Trans-shipment may occur at each point of transfer and there is usually a tremendous number of containers that must be unloaded, transferred to a temporary stack, and later loaded on to another ship, or back onto the same ship or loaded instead onto another form of transport.
A freight terminal is conventionally operated by a partly computerized Terminal Operating System (TOS) that calculates loading and unloading schedules for each container coming into or leaving the terminal, as well as for each container that has to be moved around from one stack to another in the yard of the freight terminal. The terminal operating system generally issues a work order for each time a container has to be moved and preferably the work order also identifies both the container and the vehicle that has been scheduled to transport the container.
The development of automated cranes has improved loading and unloading and made the productivity more predictable, and also eliminated many situations in which port workers have been exposed to danger and injury. Loading and unloading the ship is seen as a critical stage or a bottleneck in terms of freight handling as the ships are idle in port during the time that loading/unloading takes place. To reduce this idle time the container cranes are normally run continuously on long shifts until the loading or unloading of each ship is completed.
A container crane uses a number of powerful electric motors mounted on a hoist or spreader and on a trolley to power the moving parts and wind in or let out the wire ropes or cables used to lift up or down a spreader holding a container. Electric motors are also used to power the movements of the trolley holding the spreader to lift and transport the containers out of the ship and onto a truck chassis or a stack etc. on land, or vice versa if loading.
To achieve the shortest unloading and loading times container handling equipment has to be at least partly automated in normal operation. The width of shipping containers is standardised at 8 ft, but the height varies between from 8 and 9.5 ft. The most common standard lengths are 20 ft and 40 ft long. The 40 ft container is very common today and even longer containers up to 53 ft long are also in use. International standard dimensions are based on a number of ISO recommendations made between 1968 and 1970, and in particular a recommendation R1161 from January 1970 which made recommendations about dimensions of corner fittings for standard containers. One could say that the distances between corner fittings on standard shipping containers are standarised in accordance with the ISO recommendations. The corner fittings, also known as corner castings, include standard openings so that a container may be picked up by inserting a hook of a crane, or spreader, into each of the four corner fittings at the top of the container. The size and shape of the oval-shaped openings were defined in another standard ISO 1161 from 1984. The same type of corner fittings, eg those on the bottom of a container, may be used to lock a container in place in a position (eg in a hold or on deck) onboard a ship or on a wagon or a chassis. A vehicle chassis is commonly equipped with a number of locking devices called a twistlock. The twistlocks are arranged on the chassis to interlock with the opening in the corner fitting of each corner of the container, eg with the corners on the bottom of the container. By interlocking with the corner fittings using twistlocks in a chassis a container is securely fastened to a vehicle chassis or railway wagon etc.
Each ship-to-shore (STS) container crane and automated stacking crane (ASC) has a lifting device usually incorporating a spreader of some kind that directly contacts a container. The spreader grips the container using hooks or other fittings to engage with the standard sized opening in the corner fittings on the container, to lift it, lower it and release it. In this description the term spreader is used to denote a part of a lifting device that is in direct contact with a container. Spreaders are normally designed to handle more than one size of container, typically 20-40 ft or 20-40-45 ft long containers. A spreader may at any one time lift and handle one single 40 ft or a 45 ft container or two 20 ft containers. Modern spreaders are adjustable in use so that the same spreader can be used to pick up one 20 ft, or two 20 ft containers at a time by adjusting the length of the spreader.
U.S. Pat. No. 7,123,132 entitled Chassis alignment system, and assigned to ABB, describes a method for aligning a truck chassis with a required position relative to a crane, in which method the truck or truck chassis is scanned by a laser scanner. This method is suitable for use with a STS crane where the container load is supported on wire ropes when being hoisted and/or transported. The use of wire ropes to support a hanging load presents additional challenges of measuring and adjusting for container movement in the form of the container swaying. While a container is being lifted from the ship, moved towards the quayside and truck chassis, and subsequently lowered towards the truck chassis the container may also develop undesirable movement in the directions of skew, list and/or trim as described in U.S. Pat. No. 7,950,539 entitled: Load control device for a crane; and assigned to ABB. The crane control system currently used by ABB for the ASC cranes is in addition arranged with four downward-looking cameras mounted on the spreader. These cameras are used to provide images to a remote human operator of all four corners of a container as the container is moved towards a landing target in order to allow manual operation of the crane by the remote operator.
In the former U.S. Pat. No. 7,123,132 named above the laser scanner is located sufficiently high up on the structure of the crane such that it is able to scan a plurality of loading/unloading lanes. A truck is scanned when it enters into one of the loading/unloading lanes in order to detect/identify at least one edge of the truck. Preferably the laser scanner detects a straight edge in the form of a horizontal beam on the rear end of the chassis. The distance between the identified edge of the truck and a fixed point on the crane may be measured in one action.
U.S. Pat. No. 7,106,883 entitled: Container position measuring method and device for cargo crane and container landing/stacking method; assigned to Mitsubishi Heavy Industries Ltd, describes a method for landing a container. In particular it describes mounting one or two CCD cameras on one side of a spreader pointing downwards to make images of a container held by the spreader and/or a second container positioned below the suspended container as a landing target. Processing of image data from a CCD camera is described wherein a long edge (representing the long side) or a short edge (representing the short side—width) of a container held by a hoisting accessory (spreader) is identified, which method is referred to as “edge extraction”. When more than one long edge is identified in an image, the edge that is most long is assumed to represent the edge of the side being searched for on the held or target container. It is said that relative position for a suspended container and a target container may be detected accurately and reliably by utilizing edge extraction.
A computerized system used by ABB for autolanding a container on a chassis in a freight terminal today, called Target Positioning System (TPS), is based in part on measurements of truck chassis position made using a laser scanner that is located on the trolley of the crane. The position of a moving container held by a spreader suspended from the trolley and being landed by an STS crane may be automatically controlled and measured as previously described above.
However, as the speed with which container cranes handle containers has increased it has become more of a challenge to find the position of a chassis quickly and with high accuracy using the laser scanner mounted on the trolley of the crane. The type of vehicle chassis that are only used in the terminal area, often called a terminal chassis, may be recognized more easily by fitting such terminal chassis with container landing guides (or locating guides) with a known size and appearance, such as the terminal chassis 39 shown in FIG. 9 (Prior Art). Such guides are designed with prominent straight edges to make easily recognized targets for laser scanners. However, vehicles that travel outside of the terminal, herein called a road chassis, may not have any such standard structures fitted to them to facilitate reliable laser detection. A road chassis may present a difficult challenge in order to recognize a particular road chassis and measure a distance to it, accurately as well as quickly.
Despite the teachings of the above documents improvement in landing of containers on a vehicle chassis is still required. Improved processes for landing containers on other landing targets such as on the top container in a stack would be beneficial. A quicker or more accurate process for landing containers on a temporary or interim landing target would also be beneficial. This is so when unloading a large number of containers it is advantageous if certain containers can be landed on a temporary landing target or rack quickly by the same container crane in order that unloading is not held up by eg a landing target that is temporarily blocked. To summarise, it would be an advantage to be able to reduce the time it takes to unload containers from a ship.